1. Field of the Invention
This invention relates generally to a motorized precision spindle apparatus for rotating and automatically exchanging tools in a flexible machining operation.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Motorized spindles for rotating and automatically exchanging machine tools are known in the art. For example, the Mazak Machining Center Model FH-680X manufactured by Yamazaki Mazak Corporation, discloses such an apparatus that includes an outer cartridge spindle and a separate motor cartridge spindle. The outer cartridge spindle is removably and interchangeably supported on the motor cartridge spindle. The outer cartridge spindle includes an outer cartridge spindle shaft supported for rotation about a spindle axis within a coaxial outer cartridge spindle shaft housing on outer cartridge spindle bearings. The outer cartridge spindle bearings are operatively connected between the outer cartridge spindle shaft and the outer cartridge spindle shaft housing. A spindle motor is supported in the motor cartridge spindle and includes a motor shaft drivingly and detachably connected to an inner end of the outer cartridge spindle shaft. The Mazak machining center also includes a tool holder supported in an outer end of the outer cartridge spindle shaft. The tool holder releasably holds a tool in position for rotation with the outer cartridge spindle shaft about the spindle axis. A draw-bar is coaxially supported for reciprocal axial motion through the outer cartridge spindle shaft and the motor shaft. An outer end of the draw-bar is operably connected to the tool holder and is spring biased in an axially inward direction away from the tool holder, which causes the tool holder to grip a tool. The Mazak machining center also includes a draw-bar actuator including a hydraulic cylinder supported axially adjacent the spindle motor and operably connected to an inner end of the draw-bar. The draw-bar actuator moves the draw-bar in a direction opposite the spring bias, which releases any tool the holder may be holding. The draw-bar includes an outer draw-bar section that is housed in the outer cartridge spindle shaft and is releasably connectable end-to-end to an inner draw-bar section housed in the motor shaft.
However, the Mazak machining center is unable to move the draw-bar outward, opposite the spring bias direction, without axially loading the outer cartridge spindle bearings. This is because the detachable geared connection of the motor shaft to the outer cartridge spindle shaft provides for the transmission of torque loads only. To facilitate easy installation and removal of outer cartridge spindles, there is no provision for axially retaining the outer cartridge spindle relative to the motor shaft and the draw-bar actuator. As a result, the application of axial loads to the bearings whenever a tool is released from the outer cartridge spindle reduces bearing life and reduces the speed at which the spindle can be rotated.
What is needed is a motorized precision spindle that has an interchangeable outer cartridge spindle and a two-piece draw-bar and that can release a tool without applying axial pressure to outer cartridge spindle bearings of the spindle.